As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of batteries has also sharply increased as an energy source for the mobile devices. Also, much research on batteries satisfying various needs has been carried out.
In terms of the shape of the batteries, the demand of prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for the batteries, the demand of lithium secondary batteries, such as lithium ion polymer batteries, having high energy density, high discharge voltage, and high output stability, is very high.
Furthermore, the secondary batteries may be classified based on the construction of an electrode assembly having a cathode/a separator/an anode structure. For example, the electrode assembly may be constructed in a jelly-roll (winding) type structure in which long-sheet type cathodes and anodes are wound while separators are disposed between the respective cathodes and anodes, a stacking type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked one on another while separators are disposed between the respective cathodes and anodes, or a stacking/folding type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked one on another while separators are disposed between the respective cathodes and anodes to constitute a bi-cell or a full-cell, and then the bi-cell or a full-cell is wound.
Recently, much interest has been taken in a pouch-shaped battery having such a stacking or stacking/folding electrode assembly mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, and easy modification in shape, and, as a result, the use of the pouch-shaped battery has gradually increased.
FIG. 1 is an exploded perspective view illustrating the general structure of a conventional pouch-shaped secondary battery.
Referring to FIG. 1, the pouch-shaped secondary battery 10 includes an electrode assembly 30, electrode taps 40 and 50 extending from the electrode assembly, electrode leads 60 and 70 welded to the electrode taps 40 and 50, respectively, and a battery case 20 for receiving the electrode assembly 30.
The electrode assembly 30 is a power generating element comprising cathodes and anodes successively stacked one on another while separators are disposed between the respective cathodes and anodes. The electrode assembly 30 is constructed in a stacking structure or a stacking/folding structure. The electrode taps 40 and 50 extend from electrode plates of the electrode assembly 30. The electrode leads 60 and 70 are electrically connected to the pluralities of electrode taps 40 and 50 extending from the electrode plates of the electrode assembly 30, for example, by welding. The electrode leads 60 and 70 are partially exposed to the outside of the battery case 20. To the upper and lower surfaces of the electrode leads 60 and 70 is partially attached insulative film 80 for improving sealability between the battery case 20 and the electrode leads 60 and 70 and, at the same time, for accomplishing electrical isolation between the battery case 20 and the electrode leads 60 and 70.
The battery case 20 is made of an aluminum laminate sheet. The battery case 20 has a space for receiving the electrode assembly 30. The battery case 20 is formed generally in the shape of a pouch. In the case that the electrode assembly 30 is a stacking type electrode assembly as shown in FIG. 1, the inner upper end of the battery case 20 is spaced apart from the electrode assembly 30 such that the plurality of cathode taps 40 and the plurality of anode taps 50 can be coupled to the electrode leads 60 and 70, respectively.
FIG. 2 is an enlarged sectional view illustrating the inner upper end of the battery case of the secondary battery shown in FIG. 1, in which the cathode taps are coupled to each other in a concentrated state and connected to the cathode lead, and FIG. 3 is a front see-through view illustrating the secondary battery of FIG. 1 in an assembled state.
Referring to these drawings, the plurality of cathode taps 40, which extend from a cathode collector 41 of the electrode assembly 30, are connected to one end of the cathode lead 60, for example, in the form of a welded bunch constituted by integrally combining the cathode taps 40 with each other by welding. The cathode lead 60 is sealed by the battery case 20 while the other end 61 of the cathode lead 60 is exposed to the outside of the battery case 20. Since the plurality of cathode taps are combined with each other to constitute the welded bunch, the inner upper end of the battery case 20 is spaced a predetermined distance from the upper end surface of the electrode assembly 30, and the cathode taps 40 combined in the form of the welded bunch are bent approximately in the shape of V. Hereinafter, the coupling region between the electrode taps and the electrode lead will be referred to as a “V-form region.”
When the battery drops with the upper end of the battery, i.e., the cathode lead 60 of the battery, down, or an external physical force is applied to the upper end of the battery, however, the electrode assembly 30 moves toward the inner upper end of the battery case 20, or the upper end of the battery case 20 is crushed. As a result, the anode of the electrode assembly 30 is brought into contact with the cathode taps 42 or the cathode lead 61, and therefore, short circuits may occur inside the battery. Consequently, the safety of the battery is greatly lowered.
In order to solve the above-mentioned problem, the present invention provides a structure in which V-form regions in a receiving part of the battery case are modified into a predetermined shape.
In connection with this case, technologies for modifying the receiving part of the battery case have been proposed. As an example, Japanese Unexamined Patent Publication No. 2002-200584 discloses a structure in which pluralities of grooves and flat parts are formed along the side of a receiving part of a battery case constructed in a trapezoidal shape when viewing the vertical section of the battery case such that an electrode assembly can be brought into tight contact with the inner surface of the receiving part of the battery case. However, the disclosed technology has a drawback in that the grooves and the flat parts must be formed at the side of the battery case, which has relatively small height, and therefore, it is difficult to form the grooves and the flat parts. When using the disclosed technology, it is possible to improve the attachment of the electrode assembly to the battery case in a battery structurally having no V-form regions (for example, a prismatic jelly-roll type battery). However, it has been proved that the disclosed technology cannot prevent the movement of the electrode assembly toward the electrode taps in a battery having V-form regions for the coupling between the electrode taps and the electrode leads, as described above.
Consequently, a technology for manufacturing a battery while effectively utilizing the V-form regions, which do not contribute to the capacity and the operation of the battery, and preventing the occurrence of short circuits due to the movement of the electrode assembly is highly required.